docs: def storage_color(self, user_storage):
          """
          Return labels indicating amount of storage used.
          """
          p = user_storage.percentage
          if p >= 0 and p < 60:
              return "success"
          if p >= 60 and p < 90:
              return "warning"
          if p >= 90 and p <= 100:
              return "danger"
          raise ValueError("percentage out of range")